The present invention relates to a reduction resistive dielectric ceramic composition containing therein ceramic grains of a core-cell structure and a ceramic capacitor including therein dielectric layers made by using such a ceramic composition.
Recently, a base metal, e.g., Ni, has been widely used in forming internal electrodes of a multilayer ceramic capacitor for the purpose of reducing manufacturing costs and various reduction resistive dielectric ceramic compositions capable of being sintered simultaneously with the internal electrode composed of the base metal have been developed. One of the reduction resistive dielectric ceramic compositions is a barium titanate-based dielectric ceramic composition including ceramic grains of a core-shell structure.
However, in case where a multilayer ceramic capacitor, which fulfils the X7R characteristic (EIA standards) and the B characteristic (EIAJ standards), is manufactured by employing a barium titanate-based dielectric ceramic composition having a dielectric constant equal to or greater than 3000 and internal electrodes composed of the base metal such as Ni, its accelerated life and temperature characteristics become unacceptably deteriorated.
It is therefore, an object of the present invention to provide a ceramic capacitor exhibiting such electric characteristics as an accelerated life equal to or greater than 200,000 seconds, a capacitance variation not smaller than xe2x88x9210% at 85xc2x0 C. (compared with that obtained at a temperature of 20xc2x0 C.) and not smaller than xe2x88x9215% at 125xc2x0 C. (compared with that obtained at a temperature of 25xc2x0 C.), and tan xcex4 of 3.5% or less, wherein the ceramic capacitor is manufactured by employing a reduction resistive dielectric ceramic composition possessing a high dielectric constant equal to or greater than 3000.
In accordance with one aspect of the invention, there is provided a dielectric ceramic composition including: sintered ceramic grains having a core-shell structure, wherein 50%xcx9c80% of the grains have a domain width of twin smaller than 20 nm; not greater than 30% of the grains have a domain width of twin in the range from 20 nm to 50 nm; not smaller than 10% of the grains have a domain width of twin greater than 50 nm or have no twin.
In accordance with another aspect of the invention, there is provided a ceramic capacitor including: more than one internal electrodes; and one or more dielectric layers composed of a dielectric ceramic composition, each of the dielectric layers being sandwiched between two neighboring internal electrodes, wherein the dielectric ceramic composition includes sintered ceramic grains having a core-shell structure, wherein 50%xcx9c80% of the grains have a domain width of twin smaller than 20 nm; not greater than 30% of the grains have a domain width of twin in the range from 20 nm to 50 nm; not smaller than 10% of the grains have a domain width of twin greater than 50 nm or have no twin.